You are inventing definitions here. > System on Chip are called System on Chip because they don’t expose I/O ports(like PORTA through PORTD on AVR) to the pins

You are inventing definitions here. > System on Chip are called System on Chip because they don’t expose I/O ports(like PORTA through PORTD on AVR) to the pins thus can’t interface RAM or ROM or other peripherals natively, but only over narrower buses through internal interface chips/logics. What does IO port multiplexing of the AVR have to do with the definition of SoC? > In my rule of thumb, every surface mounted “CPU” between 80 to 200MHz across industries were called SoC from 2003 through 2010s. No. I dont see how the physical mounting of the package changes anything. Most processors are surface mount, even some bga x86 chips. > Those CPUs/MPUs that do expose I/O directly to be interfaced to SDRAM, LCD or equivalents of North Bridge chip on PC were usually called either MPU or CPU, often MPU for they integrate some peripherals. No. MPU = MicroProcessor Unit. > Those under 80-120MHz were often called Microcontrollers(uC). They were also often self contained like SoC but didn’t count, also got a lot higher clocked recently but still don’t. So modern highly integrated microcontrollers, an effective system on a chip with 300+MHz core speed, sram, flash, eeprom, can, uarts, ethernet, pwm, counters, dac's, adc's, arent system on chips? > SoC means CPU’s main I/O ports are not exposed to pins. Uh, No.